Aylesbury, Marlow, East Hyde and Bishop Stortford are the worst-hit areas, the company says. Earthing cable, lead roofs and galvanised metal grating have been ripped out of water and sewage works by criminals.
It is using “SmartWater” technology to make it easier to trace stolen metals and deter thieves.
Bob Collington, Thames Water’s director of asset management, said: “Metal theft at our sites costs our customers millions of pounds to put right. We are dealing with this by applying a forensic signature to all our equipment, so anything taken from one of our sites can be traced back. This makes it very difficult for criminals to sell on stolen items without detection.
“Any thieves who target our property face being sprayed with forensic liquid, meaning they will carry evidence of their crime on their skin and clothing wherever they go – it’s a huge risk, for very little gain.”